Bluetooth: L2CAP: Fix user-after-free

This uses l2cap_chan_hold_unless_zero() after calling
__l2cap_get_chan_blah() to prevent the following trace:

Bluetooth: l2cap_core.c:static void l2cap_chan_destroy(struct kref
*kref)
Bluetooth: chan 0000000023c4974d
Bluetooth: parent 00000000ae861c08
==================================================================
BUG: KASAN: use-after-free in __mutex_waiter_is_first
kernel/locking/mutex.c:191 [inline]
BUG: KASAN: use-after-free in __mutex_lock_common
kernel/locking/mutex.c:671 [inline]
BUG: KASAN: use-after-free in __mutex_lock+0x278/0x400
kernel/locking/mutex.c:729
Read of size 8 at addr ffff888006a49b08 by task kworker/u3:2/389

Link: https://lore.kernel.org/lkml/20220622082716.478486-1-lee.jones@linaro.org
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Sungwoo Kim <iam@sung-woo.kim>

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 770891f..1f34b82 100644 (file)
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4309,6 +4309,12 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
                }
        }
 
+       chan = l2cap_chan_hold_unless_zero(chan);
+       if (!chan) {
+               err = -EBADSLT;
+               goto unlock;
+       }
+
        err = 0;
 
        l2cap_chan_lock(chan);
@@ -4338,6 +4344,7 @@ static int l2cap_connect_create_rsp(struct l2cap_conn *conn,
        }
 
        l2cap_chan_unlock(chan);
+       l2cap_chan_put(chan);
 
 unlock:
        mutex_unlock(&conn->chan_lock);